Numerical simulation of freezing shear driven rivulets using an enthalpy method formulation

A numerical simulation of freezing shear driven rivulets is presented herein. The physics of the freezing process is captured in the simulation through application of the “enthalpy method”; a formulation well suited for the Stefan class of problems. The associated system of fully implicit finite difference equations was solved using the Gauss-Seidel iterative technique. The enthalpy method formulation is first applied to the case of a “stationary” freezing rivulet, but with a convective boundary at the free surface. The “stationary” simulation is utilized as a subset of the more complex “traveling”, or shear driven, simulation. The freezing process of shear driven rivulets was divided into three distinct modes based upon macro-scale observations of freezing rivulet flow on a NACA 0012 airfoil. From such observations, a non-dimensional empirical parameter was developed which establishes the bulk rivulet halt criterion for a freezing rivulet during runback

Scarcity and abundance of land resources: Competing uses and the shrinking land resource base

Widespread hunger and rising global food demands (FAO, 2009) require better use of the world's water, land and ecosystems. For an estimated world population of about 9 billion in 2050, agricultural production has to increase by about 70 percent globally and by 100 percent in developing countries. An enormous effort is required to achieve the implied annual growth of nearly 1.5 percent (Bruinsma, 2009; Fischer, 2009; Godfray et al., 2010). The following policy challenges are of particular concern: Agricultural water withdrawals amount to 70 percent of total anthropogenic water use, and irrigated crops account for 40 percent of the world's total production (FAO, 2003). This makes the agriculture sector of critical social importance, responsible for massive environmental impacts and vulnerable to competition for land and water resources. Land and water uses for food production regularly compete with other ecosystem services. Ignoring such conflicts over resource use and tradeoffs can lead to unsustainable exploitation, environmental degradation and avoidable long-term social costs. Overcoming this limitation requires better understanding and management of competing uses of land, water and ecosystem services. This includes robust expansion of food and bio-energy production, sustaining regulating ecosystem functions, protecting and preserving global gene pools and enhancing terrestrial carbon pools. The prospect of meeting future water demand is limited by the declining possibilities of tapping additional sources of freshwater, and by the decreasing quality of water resources caused by pollution and waste. Freshwater resources are unevenly distributed, and many countries and locations suffer severe water scarcity (MEA, 2005). Climate change is happening, and further global warming in the coming decades seems unavoidable (IPCC, 2007). Food and water provision, land management, and the protection of nature face the immediate need to develop location-specific coping strategies, to use resources differently, to reduce systemic volatility and to safeguard the full range of ecosystem services. The range of land uses for human needs is limited by environmental factors including climate, topography, and soil characteristics. Land use is primarily determined by demographic and socio-economic drivers, cultural practices and political factors, such as land tenure, markets, institutions and agricultural policies. Good quality and availability of land and water resources, together with important socio-economic and institutional factors, is essential for food security. FAO, in collaboration with IIASA, has developed a system that enables rational land-use planning based on an inventory of land resources, and evaluation of biophysical limitations and production potentials. The Agro-Ecological Zones (AEZ) approach is based on robust principles of land evaluation. The current Global AEZ (GAEZ-2009) offers a standardized framework for the characterization of climate, soil and terrain conditions relevant to agricultural production, which can be applied at global to subnational levels

Supersonic laminar flow control research

The objective of this research is to understand supersonic laminar flow stability, transition and active control. Some prediction techniques will be developed or modified to analyze laminar flow stability. The effects of distributed heating and cooling as an active boundary layer control technique will be studied. The primary tasks of the research apply to the NASA/Ames PoC and LFSWT's nozzle design with laminar flow control and are listed as follows: (1) predictions of supersonic laminar boundary layer stability and transition; (2) effects of wall heating and cooling on supersonic laminar flow control; (3) performance evaluation of the PoC and LFSWT nozzle designs with wall heating and cooling applied at different locations and various lengths; and (4) effects of a conducted -vs- pulse wall temperature distribution for the LFSWT

Key Dimension 4: Environmental Waste Security

Asia and the Pacific shows a positive trend in strengthening water security with the number of water insecure countries dropping to 29 from 38 in 2013, according to this latest edition of the Asian Water Development Outlook (AWDO). Despite this progress, enormous challenges in water security remain. Asia is home to half of the world’s poorest people. Water for agriculture continues to consume 80% of water resources. A staggering 1.7 billion people lack access to basic sanitation. With a predicted population of 5.2 billion by 2050 and 22 megacities by 2030, the region’s finite water resources will be under enormous pressure—especially with increasing climate variability. Recent estimates indicate up to 3.4 billion people could be living in water-stressed areas of Asia by 2050. With a Sustainable Development Goal dedicated to water and sanitation for all, AWDO 2016 is a tool to help assess the region’s progress in meeting this ambitious target

Accuracy assessment of ISI-MIP modelled flows in the Hidukush-Karakoram-Himalayan basins

Large Asian rivers heading in the Hindukush-Karakoram-Himalayan mountains, and whose streamflow includes significant snow-melt and glacier-melt components, may be highly susceptible to climate warming and pattern changes. Millions of people depend on these streamflows for agriculture and power generation. Reliable predictions of future water availability are therefore needed for planning under a changing climate, and depend on the quality of hydro-climatic modelling. ISI-MIP provides global hydrological modelling results, and need validation at regional scale. This study evaluates the accuracy of modelled flows from the hydrological models used in ISI-MIP, in various sub-basins of the Upper Indus Basin (UIB) and for the reference period 1985-1998. The modelled flows are based on six hydrological models, which are: i) H08, ii) VIC, iii) WaterGAP, iv) WBM, v) MPI-HM, vi) PCR-GLOBWB. Of these models, H08 and VIC are energy-based hydrological models, while the others are temperature-based hydrological models. WBM and MPI are not suitable for the UIB, due to significant under-estimation (by 70-90%) of measured flows by their modelled flows. The remaining four models provide consistent, but still significantly under-estimated flows (up to 60% of measured flows) in all sub-basins, except the Kharmong basin. Monthly differences between modelled and measured flows vary between sub-basins, but with noticeable over-estimation in winter-spring months and under-estimation during summer months. Accuracy of the bias-corrected precipitation data sets (based on five GCMs) used in the ISI-MIP hydrological models has been assessed, using a basin-wide water balance assessment method. This method shows that all precipitation data sets significantly under-estimate precipitation in the UIB, particularly in the Karakoram sub-basins. The selected ISI-MIP hydrological models have used precipitation data which are under-estimates, which may be a main reason for under-estimated flows. ISI-MIP hydrological modelling needs to use the best available precipitation data for the UIB, but other input data and calibration parameters also need revision. An important message from this study is that caution must be exercised in selecting precipitation data sets and hydrological models in alpine regions such as the Hindukush-Karakoram-Himalayas